Various technologies for preventing the adhesion of an oil stain onto a surface of a member are proposed. In particular, in an optical member including antireflection films, optical filters, optical lenses, spectacle lenses and mirrors, when used by a person, a stain such as fingerprints, sebum, sweat and cosmetics adheres thereto, whereby not only its function is reduced, but the removal of the stain is complicated. Therefore, it is desired to apply an effective stain-preventing treatment.
Also, in recent years, with the spread of mobiles, a display has been frequently used outdoors. When a mobile is used under an environment where external light is made incident, this incident light is regularly reflected on the display surface, and a problem that the reflected light is mixed with displayed light, whereby a problem that a displayed image is hardly viewed or other problem is caused. For that reason, an antireflection optical member is frequently disposed on the display surface.
As such an antireflection optical member, for example, one obtained by stacking a high refractive index layer and a low refractive index layer each composed of a metal oxide on a surface of a transparent substrate; one obtained by forming a single layer of a low refractive index layer made of an inorganic or organic fluorinated compound, etc. on a surface of a transparent substrate; and one obtained by forming a coating layer containing a transparent fine particle on a surface of a transparent plastic film substrate, thereby making external light irregularly reflect on the uneven surface are known. Similar to the foregoing optical members, when used by a person, a stain such as fingerprints and sebum is easy to adhere onto the surface of such an antireflection optical member, or only a portion where the stain has adhered becomes high in reflection, thereby causing a problem that the strain is more conspicuous. In addition thereto, there was also encountered a problem that the removal of the stain is difficult because fine irregularities are usually present on the surface of the antireflection film.
Various technologies for forming on a surface of a solid member an antifouling function having performance to make a stain hardly adhere onto the surface or to make it easy to remove an adhered stain are proposed. In particular, as a combination of an antireflection member and an antifouling member, for example, an antifouling, anti-friction material having an antireflection film composed mainly of silicon dioxide and treated with an organosilicon substituent-containing compound (see, for example, JP-A-64-86101); and an antifouling, anti-friction CRT filter in which a surface of a substrate is coated with a silanol-terminated organic polysiloxane (see, for example, JP-A-4-338901) are proposed. Also, an antireflection film containing a silane compound including polyfluoroalkyl group-containing silane compounds (see, for example, JP-B-6-29332); and a combination of an optical thin film composed mainly of silicon dioxide and a copolymer of a perfluoroalkyl acrylate and an alkoxysilane group-containing monomer (see, for example, JP-A-7-16940) are proposed.
However, the antifouling layer which is formed by a conventional method is insufficient in antifouling properties, and in particular, it is hard to wipe off a stain such as fingerprints, sebum, sweat and cosmetics. Also, in the surface treatment with a material with low surface energy, such as fluorine or silicon materials, there is a cause for fears that the antifouling performance is reduced with a lapse of time. For that reason, the development of an antifouling member with excellent antifouling properties and durability is desired.
In a resin film which is used in many ways for a surface of an optical member, etc. or an inorganic material such as glasses and metals, it is general that its surface is hydrophobic or exhibits weak hydrophilicity. When a surface of a substrate using a resin film, an inorganic material or the like is hydrophilized, adhered droplets are uniformly spread on the surface of the substrate to form a homogeneous film. Therefore, the fogging of glass, a lens or a mirror can be effectively prevented, and such is useful for preventing devitrification to be caused due to hygroscopic moisture, securing visibility in the rain or the like. Furthermore, urban soot, a combustion product contained in exhaust gases from automobiles, etc. (for example, carbon black) or a hydrophobic pollutant such as fats and oils and sealant elution components hardly adheres thereto, and even when it adheres, it is simply dropped off by rainfall or water washing. Therefore, such a material is useful for various applications.
According to a surface treatment method for achieving hydrophilization which has hitherto been proposed, for example, etching treatment and plasma treatment, though the surface is highly hydrophilized, its effect is temporary, and the hydrophilized state cannot be maintained over a long period of time. Also a surface-hydrophilic coating film using a hydrophilic graft polymer as one of hydrophilic resins is also proposed (see, for example, Article of The Chemical Daily News, dated Jan. 30, 1995). However, though this coating film has hydrophilicity to some extent, it cannot be said that the compatibility with a substrate is sufficient, and high durability is demanded.
Also, a film using titanium oxide has hitherto been known as a film with excellent surface hydrophilicity. For example, a technology for forming a photocatalyst-containing layer on a surface of a substrate to highly hydrophilize the surface corresponding to optical pumping of the photocatalyst is disclosed. It is reported that when this technology is applied to various composite materials such as glasses, lenses, mirrors, exterior materials and wet area materials, excellent antifouling properties can be imparted to such a composite material (see, for example, WO 96/29375 (corresponding to U.S. Pat. No. 6,013,372)). However, in view of the matters that a hydrophilic film using titanium oxide does not have sufficient film strength and that a hydrophilizing effect is not revealed unless it is optically pumped, there is involved a problem that a use site is limited. Therefore, an antifouling member having durability and good anti-abrasion properties is demanded.
In order to achieve the foregoing problems, it is found that a hydrophilic surface which is provided with a crosslinking structure due to hydrolysis and polycondensation of a hydrophilic polymer and an alkoxide while paying attention to a characteristic of a sol-gel organic/inorganic hybrid film exhibits excellent anti-fogging properties and antifouling properties and having good anti-abrasion properties (see, for example, JP-A-2002-361800 (corresponding to US2007/0122745A1)). A hydrophilic surface layer has such a crosslinking structure is easily obtainable by combining a specified hydrophilic polymer having a reactive group in an end thereof and a crosslinking agent.